I met plenty of different strangers from around the world through Hospitality Club (the concept later copied by CouchSurfing) and never had a bad experience. Many of my friends and family thought it was dangerous inviting strangers into your home. And maybe today it is, I'm not sure. But back then practically everyone signed up there had the same open-minded spirit, they wanted to learn about people in other countries and further intercultural understanding and friendship. I've met lots of people from very different walks of life, people I might have never otherwise talked to. This is positive diversity, when there's a shared value and people can unite around it and trust each other.
To give a negative example many people in Western societies, in their strive to not be racist, have bought into the false belief that all cultures are equal, that you're assigned one by birth and that you're not allowed to criticize the culture of "other" people. Which ironically in itself is a racist idea. This in turn has lead to political movements that consider it taboo discussing certain problems connected with topics like religion, culture and ethnicity. And it's given birth to the kind of laissez-faire multiculturalism where problems never get addressed and crime, mistrust and conflict are rampant. Because people either get divided among identity lines like you mention, or unchecked immigration gives these societies the death blow (the Western European model).